President Barack Obama hoisted a beer with a white policeman and a black professor Thursday evening, aiming to cool a dispute between the pair that ignited a national debate and threatened to damage his reputation as a politician whose appeal transcends race. Speaking in the Oval Office earlier Thursday, Mr. Obama said he was "fascinated with the fascination about this evening," calling the meeting "so hyped and so symbolic." ..The White House billed the meeting as a "teachable moment" occasioned by the July 16 arrest of Harvard professor Henry Louis Gates Jr. by Cambridge police Sgt. James Crowley after a...